1. Field of the Invention
The invention relates to methods and devices for improving the safety of flight operations of turbine-powered aircraft and the efficient maintenance of aircraft engines and auxiliary power units (APU's).
2. Description of the Related Art
Aircraft gas turbine engines particularly turbofan and APU comprise many components that require an adequate and proper maintenance to operate reliably and efficiently. In order to test or troubleshoot engine and APU components and systems, it is usually necessary to run the engine or the APU. This leads to many safety hazards around engines, APU, and aircraft and increases the use of fuel and the amount of resulting pollutants that enter the atmosphere. For example, it is not allowed (not safe and practical) to run a jet engine inside hangars, or while the aircraft is lifted on jacks (usually inside the hangar for maintenance purpose) or parked at an airport gate (unless for a limited time and engine running at low power). The use of the APU inside the hangar is not convenient and necessitates a lot of precautions. In certain airports it is permissible to run up an engine at idle only (for a ground test) and for 5 minutes at the gate, and to use APU for 15 minutes maximum during aircraft turn-around time. Because of such restrictions, safety and environmental concerns, the engine must be run up (even at high power and longer time if needed) outside of the hangar and away from the airport gate, in a cleared area, where workers and the aircraft are exposed to the elements. Additionally, while the engine is running in remote location, there is always the danger that personnel, FOD (foreign object debris) might be sucked into the engine. Performing maintenance work like leak checks especially at idle will expose the mechanic to the engine inlet suction especially if leak is situated in the fan case with open fan cowls (especially in engines with gearbox installed on the fan case): in this case the mechanic will be unaware of the limit of the safe zone around the engine because he can not see the red warning stripe that indicates the limit of the safe area (the mechanic is under the inner side of the fan cowls and the red warning stripe is on the outer side of the fan cowls). Some leak checks are performed at part power 70% N1: in this type of leak check, it is difficult to detect the leakage since the fan and the reverser cowls are closed (even for idle leak check the reverser cowls are closed). When performing engine manual start especially in the high and medium bypass ratio engines, the mechanic will be near to the engine inlet suction and in certain engines he will be ahead of the red stripe and very close the engine inlet suction. In addition during engine manual start, there is a risk of starter disintegration (uncontained starter failure) if the pilot delay or forget to inform the mechanic to close manually the start valve. Even if it is closed on time, it will be around 55-56% N2 for certain recent engines and the mechanic will be close to the engine inlet suction. Sometimes some problems especially in engine starting system (like the start valve) may occur prior the start of the shutdown engine during single or reduced engines taxiing in the taxiway and necessitate aircraft ground turn-back in the gate. Working around a running engine may lead to accidents and injuries that can be fatal mainly in the recent engines (particularly high bypass ratio and even medium bypass ratio) because they are usually fitted with large fan and without inlet guide vanes (among the recent fatal accident, a mechanic was sucked into engine during oil leak check at George Bush Intercontinental airport, Jan. 16, 2006). Personnel and objects can also be blown across the tarmac by the jet blast (high velocity). This exhaust is extremely hot and can burn workers or cause heat damage to surrounding objects.
Although in-flight shutdowns of jet engines are relatively rare, when they do occur, special attention is required to avoid compromising flight safety or causing damage to the engine and its components. In certain emergencies or abnormal flight situations (like engine fire or hydraulic loss) some of the engine components are starved of lubricants while they are still being forced to turn, possibly leading to very costly damage to these components and a probable contamination of their systems. In other cases like engine shutdown or engine flame-out, the aircraft will be affected by the loss of an important part of electric, hydraulic, and pneumatic power. At certain high altitude, the restart of the engine and the start of the APU are not usually successful, so the pilots are forced to fly at lower altitudes to restart the engine or start the APU; at low altitude and low aircraft speed the restart could be difficult at low N2 speed especially in severe inclement weather. In case of multiple or all engines flame-out (due to adverse weather conditions, fuel depletion or contamination, or volcanic ash cloud) the systems' redundancy in the present aircraft will not provide a safe flight and landing. Certain dispatch conditions affect the aircraft like: the case of a twinjet is dispatched with the start valve operating manually only, where the engine starter assisted restart is not possible in case of aircraft is out windmill start limit especially at high altitude. In case of certain abnormal flight and emergency situations (all engines flame-out, engine fire, APU automatic shutdown, etc.) or anomalies (engines bleed trip-off) there is no back-up power for pneumatic power especially for long ETOPS flights.
What is needed, then, is a modification of aircraft gas turbine engine (the turbofan, turbojet, and turboprop can be fitted with these accessories and supplied with ram air, from an operating engine, APU, or any appropriate combination of air sources) and APU components coupled with a method to allow testing and troubleshooting individual engine and APU components, and systems without running the engine or the APU while the aircraft is undergoing maintenance on the ground. What is also needed is a modification of aircraft gas turbine engine and the APU components coupled with a method that allows more optimal, less disruptive and safer procedures regarding the engine and the APU during in-flight abnormal and emergency cases, and increases system redundancy and flexibility. The present invention provides a solution to both of these needs.